This proposal has two closely related components. The first component, part A, is an attempt to see if one site-specific tumor of the central nervous system of children, the small cell tumor of the posterior fossa, is indeed more than one tumor as defined by clustering of histologic and clinical features, prognosis, and temporal trends. This study will be based on all small cell tumors of the posterior fossa removed at one institution during a 50 year interval. The second component, Part B, is a proposal to do the planning to create a consortium of investigators at several institutions and to prepare a consortium proposal. The long term goal of Part B is to create an opportunity to conduct case-control epidemiologic studies of selected central nervous system tumors of children (i.e. sufficiently many "cases" of any site-specific tumor, uniform collection of high quality data, etc.).